An open box layout is configured textually as follows: A single vertical column contains faces L, M, N, O from top to bottom. A side flap face P is attached to the left of M, and another side flap face Q is attached to the right of N. If this sheet is folded to form a closed cube box, which letter would be on the face opposite M?

In an open cube/dice folding network layout, alternate faces in a straight line are always opposite to each other when folded into a 3D box.
Looking at the vertical column consisting of L, M, N, O:

* L is alternate to N $⟹$ L is opposite N.
* M is alternate to O $⟹$ M is opposite O.

The remaining side flaps P and Q will fold up to be opposite each other. Thus, the face opposite M is O.